I havent really heard anything bad about the new 6.4's. Sure there was the dreaded flamethrowers, but that was all fixed. And I hear that taking the cab off to get to the engine only takes about an hour or two, and makes it alot simpler to work on the engine and tranny. All vehicles have some flaws in them, and you can get a good vehicle with no problems, or you can get one with problems. But the newer the vehicle the more chance there is of getting one with problems. And if fuel economy is a concern, the new 6.4's are getting 1-2 mpg less than the 6.0. Its your money, go drive both of them. If you want to mod your truck though, the 6.0 is probably better. I've driven a 6.4, and I have to say that that thing was a beast with tons of power, even though it only has 400 miles on it.